Vortex-induced motions of marine risers : straked force database extraction & transient response analysis
Name
464224397-MIT.pdf
Description
Full printable version
Size
20.83 MB
Format
Adobe PDF
Checksum (MD5)
70a2b628c3826fa851d901edcef6c1ca
Author(s)
Chasparis, Filippos
Advisor(s)
Michael S. Triantafyllou.
Alternative Title
Straked force database extraction & transient response analysis
Date Issued
2009
Publisher
Massachusetts Institute of Technology
Abstract
In part I of the thesis, we extend a methodology to extract a VIV hydrodynamic database from field data to accommodate partially straked cylinders. There are two databases, each consisting of the lift and added mass coefficients as functions of reduced velocity and amplitude of response; the first for the bare part of the riser, and the second for the straked part. First, the program VIVA together with nominal force databases obtained from laboratory hydrodynamic experiments is used in order to get an initial prediction of the riser response under a particular flow profile. The nominal databases are then altered in a systematic way until the new VIVA predicted response best matches the measured field response, thus resulting in optimal databases. In part II of the thesis, we show using experimental data on a model riser that lock-in of long flexible risers placed in sheared or uniform cross-flows is a much richer phenomenon than lock-in of flexibly-mounted rigid cylinders under similar conditions. In particular, we find that the frequency content of the riser response may be either narrow-banded around a single dominant frequency (Type I response) or distributed along a relatively broad range of frequencies (Type II response). Distinct transition from Type I to Type II response, and vice versa, can occur several times within a single experimental record. Type I responses reveal features of a quasi-periodic oscillation, often accompanied by large 3rd harmonic components in the acceleration and strain signals, increased correlation length, stable riser trajectories, and monochromatic traveling or standing waves.
(cont.) Type II responses, on the other hand, are characterized by features of chaotic oscillation with small or non-existent 3rd harmonic components in the acceleration and strain signals, reduced correlation length, and a continuous spectrum.
Description
Thesis (S.M. in Mechanical Engineering and Naval Architecture and Marine Engineering)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2009.
Includes bibliographical references (p. 55-58).
Subjects
Mechanical Engineering.
MIT Department
Massachusetts Institute of Technology. Department of Mechanical Engineering
Terms of Use
M.I.T. theses are protected by
copyright. They may be viewed from this source for any purpose, but
reproduction or distribution in any format is prohibited without written
permission. See provided URL for inquiries about permission.
copyright. They may be viewed from this source for any purpose, but
reproduction or distribution in any format is prohibited without written
permission. See provided URL for inquiries about permission.
Persistent DSpace Link
